Updated copyright information in some classes.
Added encoders for binary compatibility

- BSONEncoder,
- BasicBSONEncoder,
- DefaultDBEncoder
- BSONObjectCodec
Updated BSON class. Now it relies on BSONObjectCodec and have correct method signatures (encode(BSONObject) instead of encode(DBObject))
Fixed number of find bugs issue in BSONObjectCodec
Updated BSONDecoderTest.testDecodingNumbers

In previous revision - we used int64 for zero. Now - int32.
Refactoring and test coverage

- Renamed BSONObjectCodec to BSONObjectEncoder and made it package visible
- Made BSONCallbackAdapter package visible
- org.bson.BSON is now rely on BasicBSONEncoder and BasicBSONDecoder
- Added tests to BSONDecoderTest class
- Added tests to BSONEncoderTest class
- Remove unnecessary tests from NewBSONDecoderOldTest class